CN115987391A

CN115987391A - Free space optical communication method and device

Info

Publication number: CN115987391A
Application number: CN202111205651.0A
Authority: CN
Inventors: 陈纾悦; 宋启瑜; 黄琨
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-10-15
Filing date: 2021-10-15
Publication date: 2023-04-18
Also published as: WO2023060969A1

Abstract

The present disclosure relates to an FSO communication method and a communication apparatus thereof. The method comprises the following steps: the first FSO communication device transmits a first optical signal to the second FSO communication device; the first FSO communications device receiving a second optical signal from the second FSO communications device; and based on the second optical signal, performing at least one of the following operations using a first optical phase-controlled modulator within the first FSO communications device: a) Adjusting a light emission direction of the first optical signal to the second FSO communication device, or b) adjusting a light incidence direction of the second optical signal to a first light receiving unit within the first FOS communication device. By the FSO communication method disclosed by the invention, APT control can be realized in an optical phase control mode rather than a mechanical mode. In this way, stability problems associated with mechanical control can be avoided.

Description

Free space optical communication method and device

Technical Field

The present application relates to the field of optical communications, and more particularly, to a free space optical communication method and apparatus.

Background

The transmission of light beams in a Free Space Optical Communication (FSO) system is affected by various factors including fluctuation of atmospheric turbulence, installation errors and the like, so that the arrival angle of received light beams is shifted and the light beams are jittered. Therefore, the optical signal received at the receiving end is affected by weather, installation accuracy and other factors, and the attenuation and fluctuation of the intensity are generated. In order to ensure the stability of the link communication of the FSO system, an APT (Acquisition Pointing Tracking) system needs to be adopted to compensate the jitter and the offset of the light beam, so as to ensure the fiber coupling efficiency of the receiving end and reduce the jitter and the attenuation of the received light intensity.

The traditional APT generally adopts a mechanical control mode, and utilizes a voice coil motor, a holder or a piezoelectric ceramic PZT and other mechanical units to control the high-speed deflection of a galvanometer so as to change the transmission direction of light beams, thereby ensuring the intensity of optical signals coupled into optical fibers at an FSO receiving end and reducing the light beam jitter and signal intensity jitter attenuation correspondingly generated by the receiving end due to the influence of turbulence.

Disclosure of Invention

It is an object of the present disclosure to provide an improved FSO communications method and apparatus that may enable more stable APT control.

According to a first aspect of the present disclosure, there is provided an FSO communication method performed by a first free-space optical FSO communication device. The method comprises the following steps: the first FSO communication device transmits a first optical signal to a second FSO communication device; the first FSO communications device receiving a second optical signal from the second FSO communications device; and based on the second optical signal, performing at least one of the following operations using a first optical phase-controlled modulator within the first FSO communications device: a) Adjusting a light emission direction of the first optical signal to the second FSO communication device, or b) adjusting a light incidence direction of the second optical signal to a first light receiving unit within the first FOS communication device.

By the FSO communication method disclosed by the invention, APT control can be realized in an optical phase control mode rather than a mechanical mode. In this way, the stability problem of the mechanical control mode can be avoided, and the precision is high. In addition, the mode also contributes to integration and miniaturization.

In some embodiments, the first light signal includes first beacon light and first signal light, and the second light signal includes second beacon light and second signal light. In some embodiments, receiving the second optical signal originating from the second FSO communications device comprises: splitting the received second light signal via a signal beacon splitter to form split second beacon light and second signal light; and detecting the second beacon light that is split. In these embodiments, the beacon light may be multiplexed to feedback the amount of beam alignment deviation detected at the receiving end; and the signal light can be used for high-speed optical communication.

In some embodiments, adjusting the light emission direction comprises: obtaining peer bias amount information relating to light reception by the second FSO communication device based on the detection of the second beacon light; and adjusting a light emission direction of the first optical signal to the second FSO communications device using a first optical phase control modulator within the first FSO communications device based on the peer offset information. In these embodiments, the first FSO communications device may correct the direction of light emission to the second FSO communications device by means of the fed back peer offset, which embodies the concept of APT adjustment at the originating side.

In some embodiments, transmitting the first optical signal from the first FSO communications device to the second FSO communications device comprises: determining a home offset amount related to light reception of the first FSO communications device based on detection of the second beacon light; modulating the home offset into the first beacon light; combining both the modulated first beacon light and the first signal light to form the first light signal; and transmitting the first optical signal to the second FSO communications device via the first optical phase-controlled modulator. In these embodiments, the second FSO communications device may correct the direction of light emission to the first FSO communications device by means of the fed back home offset, which also embodies the concept of APT adjustment at the originating side.

In some embodiments, adjusting the light incidence direction comprises: obtaining home run-out information relating to optical reception by the first FSO communications device based on detection of the second beacon light in the second optical signal; and adjusting a light incidence direction of the second optical signal to the first light receiving unit using a first optical phase control modulator within the first FSO communication device based on the home deviation amount information. In these embodiments, the adjustment of the light incidence direction may be performed directly by the first FSO communication device as the receiving end, thereby implementing APT control at the receiving end.

In some embodiments, transmitting the first optical signal from the first FSO communications device to the second FSO communications device comprises: adjusting the polarization states of both the first beacon light and the first signal light to form a circularly polarized first light signal; and transmitting the circularly polarized first optical signal to the second FSO communications device. In the embodiments, the characteristic that circular polarization still keeps circular polarization after being transmitted through the atmosphere is skillfully utilized.

In some embodiments, receiving the second optical signal comprises: receiving the second optical signal as circularly polarized light originating from the second FSO communications device; converting the second optical signal into a second optical signal with a line bias; (ii) injecting the linearly polarized second optical signal into the first optical phase modulator; and receiving the biased second optical signal via a first optical phase-controlled modulator. In these embodiments, circular polarization is converted to linear polarization to meet the requirements for single polarization operation of the optical phase control modulator.

In some embodiments, the signal beacon splitter is positioned in the optical path downstream of the first optical phase modulator to receive the second optical signal originating from the first optical phase modulator.

In some embodiments, the first light signal comprises only a first beacon light and the second light signal comprises only a second beacon light. It will be readily appreciated that embodiments are also possible when only the beacon light is included in the optical signal, which may be implemented, for example, in an FSO communications scheme that employs beacon light for pre-alignment.

In some embodiments, the first optical phase-control modulator is a liquid crystal on silicon LCOS.

According to a second aspect of the present disclosure, a first free-space optical FSO communications device is provided. The device comprises: a first optical transmission unit for transmitting the first optical signal to the second FSO communication device; a first optical receiving unit for receiving a second optical signal originating from the second FSO communication device; and a first optical phase-controlled modulator, disposed downstream of the first light-emitting unit in an optical path, for adjusting a light-emitting direction of the first optical signal based on the received second optical signal; or the optical path upstream of the first light receiving unit, for adjusting the light incidence direction of the second light signal to the first light receiving unit based on the received second light signal.

In some embodiments, the first optical signal comprises a first beacon light and a first signal light, and the second optical signal comprises a second beacon light and a second signal light.

In some embodiments, in a case where the first optical phase modulator is disposed downstream of an optical path of the first light emitting unit, the first light emitting unit includes: a first signal light emitting unit for emitting first signal light; a first beacon light emitting unit for emitting first beacon light; and a beam combiner for combining the first signal light and the first beacon light to form the first signal light, and making the first signal light incident on the first optical phase-controlled modulator.

In some embodiments, further comprising a first light detection unit to determine peer offset information relating to light reception by the second FSO communications device based on detection of a second beacon light in the second optical signal; the first optical phase control modulator is used for adjusting the light emission direction of the first optical signal to the second FSO communication device based on the opposite-end deviation amount information.

In some embodiments, the first light detection unit is further configured to determine a home offset amount related to light reception by the first FSO communications device based on detection of a second beacon light in the second optical signal; the first beacon light emitting unit is used for modulating the local deviation value into the first beacon light.

In some embodiments, in a case where the first optical phase modulator is disposed upstream of the optical path of the first light receiving unit, the first light emitting unit includes: a first signal light emitting unit for emitting first signal light; a first beacon light emitting unit for emitting a first beacon light; and a first 1/4 wave plate for converting both the first signal light and the first beacon light into circularly polarized light to form circularly polarized first signal light.

In some embodiments, further comprising: and the second 1/4 wave plate is positioned on the optical path upstream of the first optical phase-controlled modulator and used for receiving the circularly polarized second optical signal from the second FSO communication device, converting the circularly polarized second optical signal into a linearly polarized second optical signal and then enabling the linearly polarized second optical signal to be incident to the first optical phase-controlled modulator.

In some embodiments, the first light receiving unit includes a signal beacon light splitter positioned in the optical path downstream of the first optical phase control modulator to receive the second light signal incident from the first optical phase control modulator and split the second light signal into a second beacon light and a second signal light.

In some embodiments, further comprising a first beacon light detection unit for detecting the second beacon light to obtain home run-out information relating to light reception by the first FSO communications device; the first optical phase modulator is adapted to adjust a light incidence direction of the second optical signal to the first light receiving unit based on the home deviation amount information.

In some embodiments, the first optical signal comprises only a first beacon light and the second optical signal comprises only a second beacon light.

According to a third aspect of the present disclosure, there is provided an FSO communication system. The system comprises a first FSO communications device according to the first aspect.

Drawings

The above and other features, advantages and aspects of embodiments of the present disclosure will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings. In the drawings, like or similar reference characters designate like or similar elements, and wherein:

fig. 1 shows a block diagram of a tracking control system of a prior art FSO communication system.

Fig. 2 shows a prior art tracking control architecture diagram of another FSO communications system.

Fig. 3 shows a schematic block diagram of an FSO communication system according to a first exemplary embodiment of the present disclosure.

Fig. 4 shows a schematic block diagram of an FSO communication system according to a second exemplary embodiment of the present disclosure.

Fig. 5 shows a flowchart schematic of an FSO communication method performed by the first FSO communication device (or first FSO terminal) of the present disclosure.

Detailed Description

Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present disclosure are shown in the drawings, it is to be understood that the present disclosure may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided for a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the disclosure are for illustration purposes only and are not intended to limit the scope of the disclosure.

As described in the background, conventional APT is typically mechanically controlled. For example, patent publication No. CN110233664a discloses a tracking control system and a tracking control method for wireless optical communication, the system structure of which is shown in fig. 1, a receiving end obtains the intensity of a received signal through a CCD receiving and sensing unit, and combines with GPS position information according to the signal intensity, and calculates and analyzes the alignment deviation amount at the receiving end and the transmitting end in real time through an algorithm, and feeds back the deviation amount to a transmitting end through a GPRS wireless communication module, and a servo control processing unit at the transmitting end correspondingly controls a two-dimensional servo turntable and a piezoelectric micro-motion platform to perform precise adjustment according to a feedback control algorithm after receiving the deviation amount information transmitted by the opposite end, and changes the emitting direction of emitted light at high speed in real time, thereby completing the alignment and tracking at the receiving end, and keeping the optical signal at the receiving end stable. As can be seen from the above description, this system utilizes a mechanical two-dimensional servo turntable and a piezoelectric micromotion stage as the tracking control unit.

For another example, patent publication No. CN106767543B discloses a light spot alignment method based on a four-quadrant detector, as shown in fig. 2, an incident light beam 1 is focused on a photosensitive surface of the four-quadrant detector 5 through

lens assemblies

2 and 4, the four-quadrant detector 5 converts a received optical signal into four electrical signals, amplifies the four electrical signals by an amplifying circuit 6, and transmits the four electrical signals to a signal processing unit 7 and a display screen 9, and the amplified four electrical signals are sequentially subjected to a/D conversion and kalman filtering processing in the signal processing unit 7; and (4) performing self-adaptive threshold judgment on the four processed signals, and controlling the holder 8 to act according to the judgment result, so as to adjust the position of an incident beam and realize the alignment of an incident light spot. As is apparent from the above description, this method employs a mechanical pan/tilt head as a tracking control unit.

However, a general problem with the conventional APT technique described above is that: the mechanical control mode has the stability problem, and the control precision cannot be stably guaranteed under long-time work; meanwhile, a mechanical part is adopted to control the mode of the vibrating mirror, and the volume of the APT module is relatively large.

The purpose of the present disclosure is to provide an improved APT technique for FSO communication, which does not employ mechanical control, so that the problems of poor long-term stability and unsuitability of precision of mechanical control can be avoided, and integration and miniaturization can be facilitated. To this end, the present disclosure proposes for the first time the concept of using an optical phase-control modulator for APT control of an incident and/or an emergent beam. By way of example, the optical phase-controlled modulator may be a Liquid Crystal On Silicon (LCOS). It is readily understood that other modulators suitable for optical phase control are within the scope of the present disclosure.

Fig. 3 shows a schematic block diagram of an FSO communication system according to a first exemplary embodiment of the present disclosure. As shown in fig. 3, the FSO communication system 100 may include a first FSO communication device 100 (or "first FSO terminal") and a second FSO communication device 200 (or "second FSO terminal") in free-space optical communication with each other. It is understood that the first FSO communications device 100 and the second FSO communications device 200 may be the same or different. For convenience, only examples of the first FSO communication device 100 and the second FSO communication device 200 having the same structure are shown below, and emphasis is placed only on the description of the first FSO communication device 100.

The first FSO communication device 100 may comprise a first light emitting unit 210, a first light receiving unit 220 and a first optical phase-controlled modulator 230, a first light detecting unit 240 and a first transceiving port 250.

As shown in fig. 3, the first light emitting unit 210 may include a beacon light emitting unit 211 and a signal light emitting unit 212, wherein the beacon light emitting unit 211 is adapted to emit beacon light and the signal light emitting unit 212 is adapted to emit signal light. As an example, the beacon light emitting unit 211 and the signal light emitting unit 212 may each be a laser. As will be understood from the description below, the beacon light used in the present disclosure may be multiplexed for low-speed communication to feed back the amount of beam alignment deviation at the receiving end; and the signal light may be used for high-speed optical communication. In general, the wavelengths of both the beacon light and the signal light are different, which facilitates the beam splitting process of both the beacon light and the signal light. As an example, the wavelength of the signal light may be 1550nm, for example, and the wavelength of the beacon light may be 800nm.

The first optical phase modulator 230 is disposed downstream of the first light emitting unit 210 in the optical path, and is used to manipulate the transmission direction of the light beam. As a typical example, it may be, for example, LCOS (liquid crystal on silicon). Generally, the LCOS is typically used in applications such as televisions, projectors, etc. and the principle thereof is that LCOS liquid crystal molecules are deflected by different angles by performing different voltage modulation on the LCOS, so as to form a phase difference in adjacent pixel areas, and the exit direction of incident light passing through an LC0S chip is changed by a grating diffraction effect. However, to the best of the inventors' knowledge, there is currently no application of the optical phase control modulator 230, such as LCOS, in FSO communication systems.

In some embodiments, the first optical phase-controlled modulator 230 has a requirement to operate with single polarization (i.e., with linear polarization). Therefore, the first light emitting unit 210 may further include a polarizer/beam combiner 213, wherein the polarizer/beam combiner 213 may be a combination of a polarizer and a beam combiner. In some embodiments, the polarizer/combiner 213 may allow both the signal light and the beacon light to be combined to form the first optical signal before polarizing the first optical signal to produce the line-polarized first optical signal. In still other embodiments, the polarizer/combiner 213 may polarize both the signal light and the beacon light separately before combining the linearly polarized signal light and the beacon light to form the linearly polarized first optical signal. A first optical phase modulator 230, such as LCOS, may receive the line-shifted first optical signal.

It will be readily appreciated that by controlling the operating voltage of the first optical phase modulator 230, the direction of deflection of the first optical signal, and thus the direction of light emission of the first optical signal to the second FSO communications device, may be controlled.

The first optical signal exiting the first optical phase modulator 230 may be directed to the second FSO communications device 300 via the first transceiver port 250. In some embodiments, the first transceiver port 250 may comprise, for example, a scaled beam unit 252, which may comprise, for example, a collimating lens, a telescope head, etc., whereby the first optical signal exiting the first optical phase modulator 230 may be directed to the second FSO communications device 300 via the scaled beam unit 252. In some embodiments, the first transceiving port 250 may further include a transceiving splitting unit 251, and the transceiving splitting unit 251 may be advantageous in that transceiving beams may be separated along different optical paths in the device, thereby facilitating signal processing. In the exemplary embodiment of fig. 3, the first optical signal exiting the first optical phase control modulator 230 will thus be directed to the second FSO communications device 300 via the transmit and receive beam splitting unit 251, the zoom beam unit 252. It will be readily understood that in other embodiments, it is also possible to have the transmit and receive beams processed along separate paths using separate devices, and in this case, the transmit and receive beam splitting unit 251 may be omitted. However, in order to reduce the number of optical devices, it is obviously advantageous to share the transceiving beam splitting unit 251 and the zoom beam unit 252 for transceiving two optical beams.

At the same time, the first transceiver port 250 also receives the second optical signal from the second FSO communications device 300. Similar to the first optical signal transmitted by the first FSO communications device, the second optical signal may include both the second signal light and the second beacon light. In some embodiments, the second optical signal may be incident to the first optical receiving unit 220 via the first transceiving port 250.

The first light receiving unit 220 may include a light receiving device 221, such as an optical fiber or a photodetector, for enabling coupled reception or detection of the second signal light in the second optical signal from the second FSO communication device 300. In some embodiments, the first light receiving unit 220 may further include a signal beacon splitter 222 for splitting the second signal light and the second beacon light in the second light signal, so as to conveniently separate both the second signal light and the second beacon light for subsequent processing.

The first light detection unit 240 may be used to detect the above-mentioned split second beacon light. It will be readily appreciated that when they transmit between the first FSO device and the second FSO device, their own transmission direction offsets will reflect the misalignment of the optical communications between the first FSO device and the second FSO device, whether they are the first beacon light or the second beacon light. According to the design of the present disclosure, once the above-mentioned alignment deviation amount is obtained by detecting the beacon light at the home terminal, the home terminal may modulate the alignment deviation amount onto the beacon light it transmits, and then transmit to the opposite terminal. Thus, a beacon light designed according to the present disclosure also serves to feed back the above-described amount of alignment deviation to each other at both ends of FSO communications.

Note that: the terms "home" (including "home offset") and "peer" (including "peer offset") as referred to herein may refer to both the first FSO communications device and the second FSO communications device, depending on whether the usage is from the perspective of the first FSO communications device or the second FSO communications device. For example, if from the perspective of the first FSO communication device, the first FSO communication device is the home terminal, the alignment deviation amount related to the optical reception of the first FSO communication device is the home terminal deviation amount, and the second FSO communication device is the opposite terminal, the alignment deviation amount related to the optical reception of the second FSO communication device is the opposite terminal deviation amount, and vice versa.

In some embodiments, the first light detection unit 240 may include a beacon light detection unit 242 and a position deviation detection unit 241. The beacon light detection unit 242 may be configured to detect a characteristic (e.g., light intensity) of the split second beacon light (e.g., analyze the spot centroid) to obtain a detection result, and/or decode information modulated on the second beacon light to obtain an amount of peer bias related to light reception by the second FSO communications device. As an example, the beacon light detection unit 242 may employ a CCD camera or a four-quadrant detector.

The positional deviation detection unit 242 may perform the following two functions:

a) Receiving the above-mentioned peer deviation amount information, generating an APT control signal based on the peer deviation amount, and applying a corresponding control voltage to the first spatial light modulator 230 so as to perform deflection adjustment on the outgoing light beam to the second FSO communication device 300.

b) The received beacon light detection unit 242 calculates the local deviation amount of the light beam alignment by a corresponding algorithm from the detection result of the second beacon light, and supplies the local deviation amount to the first beacon light emitting unit 211, so that the first beacon light emitting unit 211 modulates the local deviation amount onto the first beacon light to be emitted.

Although the above embodiments describe using two devices, the beacon light detection unit 242 and the positional deviation detection unit 241, in some embodiments, the functions of both the beacon light detection unit 242 and the positional deviation detection unit 241 may be implemented using only the beacon light detection unit 242.

From the above description, it is easily understood that the peer deviation amount in the above a) reflects the reception alignment deviation of the second FSO communication device (i.e., the peer), and the alignment deviation of the second FSO communication device can be compensated by adjusting the light emission direction of the first FSO communication device (i.e., the home terminal), so that when the adjustment of the emission direction is performed using the first spatial light modulator 230 in the first FSO communication device, the APT control at the originating terminal is realized.

The home offset in b) above reflects the receive alignment offset of the first FSO communications device (i.e., home). The home offset may be transmitted to the second FSO device along with the first beacon light, thereby enabling feedback of the home offset to the peer.

The second FSO device 300 may operate in a manner similar to the second FSO device 200 and will not be described again.

By using the exemplary embodiment of fig. 3, it can be understood that, during the FSO communication process, both ends of the FSO communication system may continuously receive alignment deviation amount information fed back from the opposite end via the beacon light, where the alignment deviation amount information reflects the influence of atmospheric turbulence, or light source itself jitter, etc. on light reception, and both ends may adjust their light emission directions according to the fed back alignment deviation amount information, thereby implementing stable FSO optical communication.

Fig. 4 shows a schematic block diagram of an FSO communication system according to a second exemplary embodiment of the present disclosure. As shown in fig. 4, the FSO communication system 400 may include a first FSO communication device 500 (or "first FSO terminal") and a second FSO communication device 600 (or "second FSO terminal") in free-space optical communication with each other. It is understood that the first FSO communications device 500 and the second FSO communications device 600 may be the same or different. For convenience, the following is shown only with the first FSO communication device 500 and the second FSO communication device 600 having the same structure as an example, and emphasis is placed only on the description of the first FSO communication device 500.

The first FSO communication device 500 may comprise at least a first light emitting unit 510, a first light receiving unit 520 and a first optical phase-controlled modulator 530, a first light detecting unit 540 and a first transceiving port 550.

As shown in fig. 4, similar to the embodiment of fig. 3, the first light emitting unit 510 may include a beacon light emitting unit 511, a signal light emitting unit 512, wherein the beacon light emitting unit 511 is adapted to emit beacon light, and the signal light emitting unit 512 is adapted to emit signal light. As an example, the beacon light emitting unit 511 and the signal light emitting unit 512 may be both lasers. In general, the wavelengths of both the beacon light and the signal light are different, which contributes to the beam splitting process of both the beacon light and the signal light. As an example, the wavelength of the signal light may be 1550nm, for example, and the wavelength of the beacon light may be 800nm. However, this is not a limitation, and in some embodiments it is also possible that the wavelengths of both the beacon light and the signal light are the same.

However, unlike the embodiment of fig. 3, the first light emitting unit 510 may further include a 1/4 wave plate/beam combiner 513, wherein the 1/4 wave plate functions to convert light emitted from both the beacon light emitting unit 511 and the signal light emitting unit 512 into circularly polarized light to form circularly polarized first signal light. Here, the 1/4 waveplate/beam combiner 513 may be a combination of both the first 1/4 waveplate and the beam combiner. In some embodiments, the 1/4 waveplate/beam combiner 513 may allow both the signal light and the beacon light to be combined to form the first optical signal before polarization state modulation of the first optical signal to produce the circularly polarized first optical signal. In still other embodiments, the 1/4 waveplate/beam combiner 513 may first perform polarization state modulation on both the signal light and the beacon light, respectively, and then combine the circularly polarized signal light and the circularly polarized beacon light to form the circularly polarized first light signal. In particular, in some embodiments, in order to better generate circular polarized light, a polarizer 514 may be further disposed between both the beacon light emitting unit 511 and the signal light emitting unit 512 and the 1/4 wave plate/beam combiner 513, respectively, to generate linear polarized light with a more purified polarization direction. Compared with the embodiment of fig. 3 in which linear polarization is used for transmission at both ends of the FSO communication system, circular polarization can be more stable and thus more free from the influence of the atmosphere since circular polarization maintains circular polarization characteristics after transmission through the atmosphere.

The circularly polarized first signal light may be transmitted to the second FSO communication device 600 through the first transceiving port 550. In some embodiments, the first transceiver port 550 may, for example, comprise a scaled beam unit 551, which may, for example, comprise a collimating lens, a telescope head, etc., whereby the circularly polarized first optical signal exiting the first light emitting unit 510 may be directed to the second FSO communications device 600 via the scaled beam unit 551. In some embodiments, the first transceiving port 550 may further include a transceiving splitting unit 552, and the transceiving splitting unit 552 is advantageous in that the transceiving of the optical beam can be split in the device, thereby facilitating the processing of the signal. In the example embodiment of fig. 4, the circularly polarized first optical signal exiting the first light emitting unit 510 may thus be directed to the second FSO communications device 600 via the transceiving beam splitting unit 552, the scaling beam unit 551. It will be readily appreciated that in other embodiments, it is also possible to have both transmit and receive beams processed along separate paths using separate devices, and in this case, the transmit and receive beam splitting unit 552 may be omitted. However, in order to reduce the number of optical devices, it is obviously advantageous to share the transceiving beam splitting unit 552 and the zoom beam unit 551 with the transceiving two optical beams.

At the same time, the first transceiving port 550 also receives the second optical signal from the second FSO communications device 600. Similar to the circularly polarized first optical signal transmitted by the first FSO communications device, the second optical signal of the second FSO communications device 600 is also circularly polarized, which may include both the circularly polarized second signal light and the second beacon light. In some embodiments, the second optical signal may be incident to the first optical phase-controlled modulator 530 via the first transceiving port 550.

The first optical phase modulator 530 is disposed between the first light emitting unit 520 and the first transceiving port 550, for manipulating a transmission direction of the light beam. In some embodiments, the first optical phase-controlled modulator 530 has a requirement to operate with single polarization (i.e., with linear polarization). Accordingly, the first FSO communications device 500 may further include a second 1/4 wave plate 560, which may be disposed between the first transceiver port 550 and the first optical phase modulator 530, for converting the circularly polarized second optical signal received by the first transceiver port 550 into a linearly polarized second optical signal. By applying a voltage to the first optical phase modulator 530, the light incidence direction of the second optical signal to the first light emitting unit 520 via the first optical phase modulator 530 may be controlled.

The first optical receiving unit 520 includes an optical receiving device 521, such as an optical fiber or a photodetector, for implementing coupled reception or detection of the second signal light in the second optical signal from the second FSO communication apparatus 600. In some embodiments, the first light receiving unit 520 may further include a signal beacon splitter 522 for splitting the second signal light and the second beacon light in the second light signal, so as to conveniently separate both the second signal light and the second beacon light for subsequent processing.

The first light detection unit 540 may be configured to detect the split second beacon light to obtain a home offset amount related to light reception by the first FSO communication device. As an example, the first light detecting unit 540 may be a CCD or a four-quadrant detector, which may detect the light intensity of the second beacon light or analyze the spot centroid of the second beacon light, for example).

The first optical phase control modulator 530 may adjust the incidence direction of the second optical signal to the first optical receiving unit 520 based on the local deviation amount described above. That is, in contrast to the embodiment of fig. 3, APT control may be implemented at the receiving end.

The APT of the FSO communication system of the present disclosure based on an optical phase-controlled modulator such as LCOS has been described above in detail. It is easy to understand that the APT control of the FSO system based on optical phase control of the present disclosure has the following advantages: 1) The solid-state phasing of the above-described embodiment of fig. 3 is stable because: the multiplexed beacon light can be used for transmitting the alignment deviation amount of the opposite end, and the light beam is subjected to phase control modulation by using the LCOS before entering the atmosphere for transmission, so that the light phase control of the LCOS is not limited by a single-mode working mode, and the stability of APT control is ensured; in the embodiment of fig. 4 in which the polarization state is modulated by using the 1/4 wave plate, the polarization state can be restored to the linearly polarized light determined by the polarization state at the receiving end by using the characteristic that the circularly polarized light keeps circularly polarized through atmospheric transmission, so as to meet the requirement of the light-controlled single polarization operation of LCOS, for example; 2) The light control such as LCOS is adopted, the integration is good, the high integration with the semiconductor technology can be realized, and the volume is small.

A flowchart of an FSO communication method performed by the first FSO communication device (or the first FSO terminal) of the present disclosure will be briefly described below with reference to fig. 5. It will be appreciated that a second FSO communications device, which is a peer of the first FSO communications device, may proceed similarly and will not be described in detail.

As shown in fig. 5, at block 710, a first optical signal is transmitted from a first FSO communications device to a second FSO communications device. At block 720, the first FSO communications device receives a second optical signal from the second FSO communications device.

In some embodiments, the first light signal may include a first beacon light and a first signal light; the second optical signal may include a second beacon light and a second signal light. However, this is not limiting and in other embodiments it is also possible that the first light signal comprises only the first beacon light and the second light signal comprises only the second beacon light. This case may be applied, for example, in an FSO communication scheme that employs beacon light for pre-alignment.

In some embodiments, receiving the second optical signal originating from the second FSO communications device may include: splitting the received second light signal via a signal beacon splitter to form split second beacon light and second signal light; and detecting the second beacon light that is split.

As described above, APT control for the FSO communications device may be performed at the originating end or at the terminating end. There may be different operations for the originating APT control or the terminating APT control.

For example, in some embodiments (e.g., the embodiment of fig. 3) where APT control is initiated, block 710 may further include: determining a home offset amount related to light reception of the first FSO communications device based on detection of a second beacon light; modulating the home offset into the first beacon light; combining both the modulated first beacon light and the first signal light to form the first light signal; and transmitting the first optical signal to the second FSO communications device via the first optical phase-controlled modulator.

In some embodiments (e.g., the embodiment of fig. 4) where APT control is performed at the receiving end, block 710 may further include: adjusting the polarization states of both the first beacon light and the first signal light to form a circularly polarized first light signal; and transmitting the circularly polarized first optical signal to the second FSO communications device. Further, block 720 may also include: receiving the second optical signal as circularly polarized light originating from the second FSO communications device; converting the second optical signal into a second optical signal with a line bias; (ii) injecting the linearly polarized second optical signal into the first optical phase modulator; and receiving the biased second optical signal via a first optical phase-controlled modulator.

At block 730, based on the second optical signal, using a first optical phase-controlled modulator within the first FSO communications device, at least one of: a) Adjusting a light emission direction of the first optical signal to the second FSO communication device, and b) adjusting a light incidence direction of the second optical signal to a first light receiving unit within the first FOS communication device, wherein the first optical phase-controlled modulator is positioned in an optical path upstream of the first light receiving unit.

The operation of a) above means that APT control is performed at the originating side. At this time, block 730 may further include: obtaining peer deviation amount information related to light reception by the second FSO communications device based on the detection of the second beacon light; and the optical emission direction of the first optical signal to the second FSO communications device may be adjusted using a first optical phase-controlled modulator within the first FSO communications device based on the peer offset information.

The operation of b) above means that APT control is performed at the receiving end. At this time, block 730 may further include: obtaining home run-out information relating to optical reception by the first FSO communications device based on detection of the second beacon light in the second optical signal; and adjusting a light incidence direction of the second optical signal to the first light receiving unit using a first optical phase control modulator within the first FSO communication device based on the home deviation amount information.

It is readily understood that APT control of the FSO communications device may be achieved through at least one of the above-described a) and b) operations. The APT control scheme disclosed by the invention has the advantages of good stability, good integration and small volume.

Various embodiments of the present disclosure have been described above in detail. It will be understood that the above-described embodiments are illustrative or exemplary only, and are not limiting; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Further, it should be understood that the flows described above are also merely examples. Although the steps of a method are described in a particular order in the specification, this does not require or imply that all of the illustrated operations must be performed in the particular order to achieve desirable results, but rather that the steps depicted may be performed in an order that varies. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions.

In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain features are recited in mutually different embodiments or in dependent claims does not indicate that a combination of these features cannot be used to advantage. The scope of protection of the present application encompasses any possible combination of the individual features recited in the individual embodiments or in the dependent claims, without departing from the spirit and scope of the application.

Furthermore, any reference signs in the claims shall not be construed as limiting the scope of the invention.

Claims

1. An FSO communication method performed by a first free-space optical FSO communication device, comprising:

the first FSO communication device transmits a first optical signal to a second FSO communication device;

the first FSO communications device receiving a second optical signal from the second FSO communications device; and

based on the second optical signal, performing, using a first optical phase-controlled modulator within the first FSO communications device, at least one of:

a) Adjusting the direction of light emission of the first optical signal to the second FSO communication device, or

b) Adjusting a light incidence direction of the second optical signal to a first light receiving unit in the first FOS communication device.

2. The FSO communications method of claim 1, the first optical signal comprising a first beacon light and a first signal light, and the second optical signal comprising a second beacon light and a second signal light.

3. The FSO communications method of claim 2 wherein receiving a second optical signal originating from the second FSO communications device comprises:

splitting the received second optical signal via a signal beacon splitter to form split second beacon light and second signal light; and

detecting the split second beacon light.

4. The FSO communication method of claim 2 or 3, wherein adjusting the light emission direction comprises:

obtaining peer deviation amount information related to light reception by the second FSO communications device based on the detection of the second beacon light; and

adjusting a direction of light emission of the first optical signal to the second FSO communication device using a first optical phase control modulator within the first FSO communication device based on the peer offset information.

5. The FSO communications method of claim 4 wherein transmitting the first optical signal from the first FSO communications device to the second FSO communications device comprises:

determining a home offset amount related to light reception of the first FSO communications device based on detection of the second beacon light;

modulating the home offset into the first beacon light;

combining both the modulated first beacon light and the first signal light to form the first light signal; and

sending the first optical signal to the second FSO communications device via the first optical phase-controlled modulator.

6. The FSO communication method of claim 2 or 3, wherein adjusting the light incidence direction comprises:

obtaining home run-out information relating to optical reception by the first FSO communications device based on detection of the second beacon light in the second optical signal; and

adjusting a light incidence direction of the second optical signal to the first light receiving unit using a first optical phase control modulator within the first FSO communication device based on the home offset information.

7. The FSO communications method of claim 6 wherein transmitting the first optical signal from the first FSO communications device to the second FSO communications device comprises:

adjusting polarization states of the first beacon light and the first signal light to form a circularly polarized first optical signal; and

and sending the circularly polarized first optical signal to the second FSO communication device.

8. The FSO communications method of claim 6, wherein receiving the second optical signal comprises:

receiving the second optical signal originating from the second FSO communications device as circularly polarized light;

converting the second optical signal into a second optical signal with a line bias;

(ii) injecting the linearly polarized second optical signal into the first optical phase modulator; and

receiving the second optical signal that is receive-biased via a first optical phase-controlled modulator.

9. The FSO communications method of claim 8 wherein said signal beacon splitter is positioned optically downstream of said first optical phase modulator for receiving said second optical signal originating from the first optical phase modulator.

10. The FSO communications method of claim 1, the first optical signal comprising only a first beacon light, and the second optical signal comprising only a second beacon light.

11. The FSO communications method of any of claims 1-3, 5, and 7-10, wherein the first optical phase-controlled modulator is a liquid crystal on silicon, LCOS.

12. A first free-space optical FSO communications device, comprising:

a first optical transmission unit for transmitting the first optical signal to the second FSO communication device;

a first optical receiving unit for receiving a second optical signal originating from the second FSO communication device; and

a first optical phase control modulator disposed downstream of the first light emitting unit in an optical path to adjust a light emitting direction of the first light signal based on the received second light signal; or the optical path upstream of the first light receiving unit, for adjusting the light incidence direction of the second light signal to the first light receiving unit based on the received second light signal.

13. The first FSO communications device of claim 12 wherein the first optical signal comprises a first beacon light and a first signal light and the second optical signal comprises a second beacon light and a second signal light.

14. The first FSO communications device of claim 13, wherein with the first optical phase modulator disposed optically downstream of the first light emitting unit, the first light emitting unit comprises:

a first signal light emitting unit for emitting first signal light;

a first beacon light emitting unit for emitting first beacon light; and

and a beam combiner configured to combine the first signal light and the first beacon light to form the first signal light, and to inject the first signal light into the first optical phase-controlled modulator.

15. The first FSO communications device of claim 14 further comprising a first light detection unit,

the first optical detection unit is used for determining opposite-end deviation amount information related to optical reception of the second FSO communication device based on detection of second beacon light in the second optical signal;

the first optical phase control modulator is used for adjusting the light emission direction of the first optical signal to the second FSO communication device based on the opposite-end deviation amount information.

16. The first FSO communications device of claim 14, wherein the first light detection unit is further configured to determine a home offset amount related to light reception by the first FSO communications device based on detection of a second beacon light in the second light signal;

the first beacon light emitting unit is used for modulating the local deviation value into the first beacon light.

17. The first FSO communications device according to claim 13, wherein in a case where the first optical phase modulator is provided upstream in the optical path of the first optical receiving unit, the first optical transmitting unit includes:

a first signal light emitting unit for emitting first signal light;

a first beacon light emitting unit for emitting first beacon light; and

a first 1/4 wave plate for converting both the first signal light and the first beacon light into circularly polarized light to form circularly polarized first signal light.

18. The first FSO communications device of claim 17, further comprising:

and the second 1/4 wave plate is positioned on the optical path upstream of the first optical phase-control modulator and used for receiving the circularly polarized second optical signal from the second FSO communication device, converting the circularly polarized second optical signal into a linearly polarized second optical signal and then enabling the linearly polarized second optical signal to be incident to the first optical phase-control modulator.

19. The first FSO communications device according to claim 17, the first optical receiving unit comprising a signal beacon optical splitter positioned optically downstream from the first optical phase controlled modulator to receive the second optical signal incident from the first optical phase controlled modulator and split the second optical signal into second beacon light and second signal light.

20. The first FSO communications device according to any one of claims 17 to 19, further comprising a first beacon light detection unit for detecting the second beacon light to obtain home deviation amount information on light reception by the first FSO communications device;

the first optical phase control modulator is adapted to adjust a light incidence direction of the second optical signal to the first light receiving unit based on the home deviation amount information.

21. The first FSO communications device of claim 12, the first optical signal comprising only a first beacon light and the second optical signal comprising only a second beacon light.

22. The first FSO communications device of any of claims 11-19 and 21, wherein the first optical phase-controlled modulator is a liquid crystal on silicon LCOS.

23. An FSO communication system, characterized in that it comprises a first FSO communication device according to any of claims 12-22.